Catalyst composition and catalytic reduction system

ABSTRACT

A catalyst composition, a method of preparation of catalyst composition, a catalytic reduction system including the catalyst composition and a system using the catalytic reduction system are provided. The catalyst composition includes a templated amorphous metal oxide substrate, a catalyst material, and a sulfur scavenger material. The catalyst material includes a catalyst metal disposed on the templated metal oxide substrate and the sulfur scavenger includes an alkali metal.

BACKGROUND

The invention relates generally to a catalyst composition andparticularly to a catalyst composition and system for reducing nitrogenoxides (NOx) through selective catalytic reduction (SCR).

Exhaust streams generated by the combustion of fossil fuels in, forexample, furnaces, ovens, and engines, contain nitrogen oxides (NOx)that are undesirable pollutants. There is a growing need to haveefficient and robust emission treatment systems to treat the NOxemissions.

In selective catalytic reduction (SCR) using hydrocarbons (HC),hydrocarbons serve as the reductants for NOx conversion. Hydrocarbonsemployed for HC-SCR include relatively small molecules like methane,ethane, ethylene, propane, and propylene, as well as longer linearhydrocarbons like hexane, octane, etc., or branched hydrocarbons likeiso-octane. The injection of several types of hydrocarbons has beenexplored in some heavy-duty diesel engines to supplement the HC in theexhaust stream. From an infrastructure point of view, it would beadvantageous to employ an on-board diesel fuel as the hydrocarbon sourcefor HC-SCR.

Fuels, including gasoline or diesel fuels containing sulfur lead to anumber of disadvantages when trying to clean the exhaust gases by someform of catalytic after-treatment. During the combustion process, sulfurin the fuel gets converted to sulfur dioxide (SO₂), which poisons somecatalysts. Further poisoning happens from the formation of base metalsulfates from the components of a catalyst composition, which sulfatescan act as a reservoir for poisoning sulfur species within the catalyst.

When the SCR catalysts absorb the NOx in the exhaust gas, they alsoabsorb sulfur oxides (SOx) in the exhaust gas. The sulfur oxides poisonthe catalysts, and the NOx absorption performance declines as thepoisoning by SOx increases. Therefore, there is a need to reduce sulfurabsorption by the SCR catalysts and prevent catalyst degradation.

BRIEF DESCRIPTION

In one embodiment, a catalyst composition is presented. The catalystcomposition includes a templated amorphous metal oxide substrate havinga plurality of pores, a catalyst material having a catalyst metal anddisposed on the substrate, and a sulfur scavenger having an alkali metaland disposed on the substrate.

In one embodiment, a method of preparation of a catalyst composition ispresented. The method includes combining a metal oxide precursor, acatalyst metal precursor and an alkali metal precursor in the presenceof a templating agent, hydrolyzing and condensing to form anintermediate product that includes metal oxide, alkali metal oxide, andcatalyst metal, and then calcining to form a templated amorphous metaloxide substrate having a plurality of pores and includes an alkali metaloxide and catalyst metal.

In one embodiment, a catalytic reduction system is presented. Thecatalytic reduction system includes a catalyst support and a catalystcomposition disposed on a catalyst support. The catalyst compositionthat includes a templated amorphous metal oxide substrate having aplurality of pores, a catalyst material having a catalyst metal anddisposed on the substrate, and a sulfur scavenger having an alkali metaland disposed on the substrate.

In one embodiment, a system is provided. The system includes an internalcombustion engine, and a catalytic reduction system disposed to receivean exhaust stream from the engine. The catalytic reduction systemincludes a catalyst support and a catalyst composition disposed on acatalyst support. The catalyst composition includes a templatedamorphous metal oxide substrate having a plurality of pores, a catalystmaterial having a catalyst metal and disposed on the substrate, and asulfur scavenger having an alkali metal and disposed on the substrate.

In one embodiment, a method of removing sulfur from a catalyticreduction system is presented. The method includes passing an exhauststream from an internal combustion engine over a catalyst composition.The catalyst composition includes a templated amorphous metal oxidesubstrate, a catalyst material comprising a catalyst metal, and a sulfurscavenger. During operation, the exhaust stream reacts with the catalystcomposition to form sulfates; the sulfates decompose to produce sulfuroxides that are eventually removed from the catalytic reduction system.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a graph depicting the NOx reduction activity of undoped, fresh4.5 mole percent silver on templated amorphous alumina (Ag-TA) catalystcomposition;

FIG. 2 is a graph depicting the NOx reduction activity of 1 mole percentLi doped, fresh 4.5 mole percent Ag-TA, in accordance with oneembodiment of the invention;

FIG. 3 is a graph depicting the NOx reduction activity of 5 mole percentLi doped, fresh 4.5 mole percent Ag-TA, in accordance with oneembodiment of the invention;

FIG. 4 is a graph depicting the NOx reduction activity of 14 molepercent Li doped, fresh 4.5 mole percent Ag-TA, in accordance with oneembodiment of the invention;

FIG. 5 is a graph depicting the NOx reduction activity of undoped, 4.5mole percent silver on templated amorphous alumina (Ag-TA) catalystcomposition after an hour of operation;

FIG. 6 is a graph depicting the NOx reduction activity of 1 mole percentLi doped, 4.5 mole percent Ag-TA after an hour of operation, inaccordance with one embodiment of the invention;

FIG. 7 is a graph depicting the NOx reduction activity of 5 mole percentLi doped, 4.5 mole percent Ag-TA after an hour of operation, inaccordance with one embodiment of the invention;

FIG. 8 is a graph depicting the NOx reduction activity of 14 molepercent Li doped, 4.5 mole percent Ag-TA after an hour of operation, inaccordance with one embodiment of the invention;

FIG. 9 is a graph depicting the after sulfation-NOx reduction activityof undoped, fresh 4.5 mole percent silver on templated amorphous alumina(Ag-TA) catalyst composition;

FIG. 10 is a graph depicting the after sulfation-NOx reduction activityof 1 mole percent Li doped, fresh 4.5 mole percent Ag-TA, in accordancewith one embodiment of the invention;

FIG. 11 is a graph depicting the after sulfation-NOx reduction activityof 5 mole percent Li doped, fresh 4.5 mole percent Ag-TA, in accordancewith one embodiment of the invention;

FIG. 12 is a graph depicting the after sulfation-NOx reduction activityof 14 mole percent Li doped, fresh 4.5 mole percent Ag-TA, in accordancewith one embodiment of the invention;

FIG. 13 is a graph depicting the after sulfation-NOx reduction activityof undoped, 4.5 mole percent silver on templated amorphous alumina(Ag-TA) catalyst composition after an hour of operation, in accordancewith one embodiment of the invention;

FIG. 14 is a graph depicting the after sulfation-NOx reduction activityof 1 mole percent Li doped, 4.5 mole percent Ag-TA after an hour ofoperation, in accordance with one embodiment of the invention;

FIG. 15 is a graph depicting the after sulfation-NOx reduction activityof 5 mole percent Li doped, 4.5 mole percent Ag-TA after an hour ofoperation, in accordance with one embodiment of the invention;

FIG. 16 is a graph depicting the after sulfation-NOx reduction activityof 14 mole percent Li doped, 4.5 mole percent Ag-TA after an hour ofoperation, in accordance with one embodiment of the invention;

FIG. 17 is a comparative graph depicting amount of HCN during operationof catalytic reduction system using undoped and 1 mole percent Li dopedAg-TA, in accordance with one embodiment of the invention; and

FIG. 18 is a comparative graph depicting amounts of CH₃CHO and HCHOduring operation of catalytic reduction system using undoped and 1 molepercent Li doped Ag-TA, in accordance with one embodiment of theinvention.

DETAILED DESCRIPTION

The systems described herein include, without limitation, embodimentsthat relate to a catalyst composition, and embodiments that relate to acatalytic reduction system including the catalyst composition and to asystem using the catalytic reduction system for reducing nitrogenoxides. Generally disclosed is a NOx reduction catalyst and NOxreduction system for reducing NOx in exhaust gas discharged from acombustion device. Suitable combustion devices may include furnaces,ovens, or engines.

In the following specification and the claims that follow, the singularforms “a”, “an” and “the” include plural referents unless the contextclearly dictates otherwise.

As used herein, a catalyst is a substance that can cause a change in therate of a chemical reaction. The catalyst may participate in thereaction and get regenerated at the end of the reaction. “Templating”refers to a controlled patterning; and, “templated” refers to determinedcontrol of an imposed pattern and may include molecular self-assembly.The method of templating and templated patterns are described in USpublications 2010/0233053 A1 and 2010/0196263 A1, which are incorporatedherein by reference. “Amorphous” refers to material characterized by alack of the long-range order generally observed for crystallinesubstances.

A “monolith” as used herein includes a ceramic block having a number ofchannels, and may be made by extrusion of clay, binders and additivesthat are pushed through a dye to create a structure. Approximatinglanguage, as used herein throughout the specification and claims, may beapplied to modify any quantitative representation that could permissiblyvary without resulting in a change in the basic function to which it isrelated. Accordingly, a value modified by a term such as “about” is notto be limited to the precise value specified. In some instances, theapproximating language may correspond to the precision of an instrumentfor measuring the value. All temperatures given herein are for theatmospheric pressure. One skilled in the art would appreciate that theboiling points can vary with respect to the ambience pressure of thefuel.

In one embodiment, a composition is presented. The composition includesa templated amorphous metal oxide substrate having a plurality of pores,and a catalyst material and a sulfur scavenger disposed on thesubstrate. The catalyst material includes a catalyst metal and thesulfur scavenger includes an alkali metal. As used herein, the amount ofcatalyst metal and alkali metal are presented as percentages of thesubstrate. Unless otherwise mentioned, the percentages presented hereinare in mole percent. The mole percentage is the fraction of moles ofdopant element out of the moles of the templated substrate. For example,in Ag-TA (silver-templated alumina), silver is presented as a fractionof moles of templated alumina (Al₂O₃).

The substrate may include an inorganic material. Suitable inorganicmaterials may include, for example, oxides, carbides, nitrides,hydroxides, carbonitrides, oxynitrides, borides, or borocarbides. In oneembodiment, the inorganic oxide may have hydroxide coatings. In oneembodiment, the inorganic oxide may be a metal oxide. The metal oxidemay have a hydroxide coating. Other suitable metal inorganics mayinclude one or more metal carbides, metal nitrides, metal hydroxides,metal carbonitrides, metal oxynitrides, metal borides, or metalborocarbides. Metallic cations used in the foregoing inorganic materialscan be transition metals, alkali metals, alkaline earth metals, rareearth metals, or the like.

In one embodiment, the catalyst substrate includes oxide materials. Inone embodiment, the catalyst substrate includes alumina, zirconia,silica, zeolite, or any mixtures comprising these elements. Suitablesubstrate materials may include, for example, aluminosilicates,aluminophosphates, hexaaluminates, zirconates, titanosilicates,titanates, or a combination of two or more thereof. In one exemplaryembodiment, the metal oxide is an aluminum oxide. In other embodiments,other substrates may be suitable and can be selected based on end-useparameters.

In one embodiment, the substrate is in the form of a powder. The desiredproperties of the catalyst substrate include, for example, a relativelysmall particle size and high surface area. In one embodiment, the powderof the catalyst substrate has an average diameter that is less thanabout 100 micrometers. In one embodiment, the average diameter is lessthan about 50 micrometers. In a further embodiment, the average diameteris from about 1 micrometer to about 10 micrometers. The catalystsubstrate powder may have a surface area greater than about 100 m²/gram.In one embodiment, the surface area of the catalyst substrate powder isgreater than about 200 m²/gram. In one embodiment, the surface area isin a range of from about 200 m²/gram to about 500 m²/gram, and, inanother embodiment, from about 300 m²/gram to about 600 m²/gram.

One way of forming templated substrates is by employing templatingagents. Templating agents facilitate the production of catalystsubstrates containing directionally aligned forms. The templating agentmay be a surfactant, a cyclodextrin, a crown ether, or mixtures thereof.An exemplary templating agent is octylphenol ethoxylate, commerciallyavailable as TRITON X-114®.

The catalyst substrate may have periodically arranged pores ofdetermined dimensions. The median diameter of the pores, in someembodiments, is greater than about 2 nm. The median diameter of thepores, in one embodiment, is less than about 100 nm. In someembodiments, the median diameter of the pores is in a range from about 2nm to about 20 nm. In another embodiment, the median diameter is fromabout 20 nm to about 60 nm and in yet another embodiment, the diameteris from about 60 nm to about 100 nm The pores in some embodiments have aperiodicity greater than about 50 Å. The pores in some embodiments havea periodicity less than about 150 Å. In one embodiment, the pores have aperiodicity in the range of from about 50 Å to about 100 Å. In anotherembodiment, the pores have a periodicity in the range from about 100 Åto about 150 Å.

In certain embodiments, the pore size has a narrow monomodaldistribution. In one embodiment, the pores have a pore size distributionpolydispersity index that is less than 1.5. As used herein, thepolydispersity index is a measure of the distribution of pore diameterin a given sample. In a further embodiment, the polydispersity index isless than 1.3, and in a particular embodiment, the polydispersity indexis less than 1.1. In one embodiment, the distribution of diameter sizesmay be bimodal, or multimodal.

In one embodiment, alumina, silica, or aluminum silicate is thesubstrate or framework for a NOx catalyst. The role of a substrate is to(1) provide robust support/framework at working temperature withcorrosive gas and steam and (2) provide gas channels for NOx andreductant to get in touch with the catalytic material.

Suitable catalyst metal may include one or more of gallium, indium,rhodium, palladium, ruthenium, and iridium. Other suitable catalystmetal includes transition metal elements and noble metals including oneor more of platinum, gold and silver. In one embodiment, the catalystmetal comprises silver. In one particular embodiment, the catalyst metalis substantially 100% silver.

The catalyst metal may be present in an amount of at least about 0.5mole percent of the substrate. In one embodiment, the catalyst metal ispresent in an amount equal to or greater than 3 mole percent of thesubstrate. In one embodiment, the amount of catalyst metal present isabout 6 mole percent of the catalyst substrate. In one embodiment, thecatalytic metal may be present in an amount in a range of from about 1mole percent to about 9 mole percent of the substrate.

In one embodiment, the catalyst composition includes one or more sulfurscavenger. A “sulfur scavenger” as referred herein is a sulfur-reactivematerial that preferentially reacts with sulfur, compared to thereactivity of the catalyst metal with sulfur. “Sulfur” as used hereinincludes the sulfur containing compounds such as, for example, SO₂.

Suitable sulfur scavengers of the catalyst composition include alkalimetals. In the catalyst composition, the alkali metals may be in thecompound form. The compound form of sulfur scavenger may existseparately or along with the substrate or catalyst metals. In oneembodiment, one or more of lithium, sodium, or potassium is used as asulfur scavenger. In an exemplary embodiment, the sulfur scavengerincludes lithium. In one embodiment, lithium exists as lithium oxide inthe catalyst composition. In one embodiment, lithium exists in thehydroxide form. In one more embodiment, lithium exists as lithiumaluminum oxide.

The sulfur scavenger of the catalyst composition may exist in differentforms. In one embodiment, the sulfur scavenger is in a compound formdeposited on the substrate material. In another embodiment, the sulfurscavenger cation is dissolved in the substrate material. In oneembodiment, the sulfur scavenger is dispersed in the substrate material.In one particular embodiment, the catalyst material and sulfur scavengerare dispersed in an intermixed form in the substrate material. The“intermixed form” herein refers to an arrangement wherein the catalystmaterial and the sulfur scavenger are present throughout the body ofsubstrate material.

The sulfur scavenger may be present in an amount of at least about 0.5mole percent of the substrate. In one embodiment, the sulfur scavengeris present in an amount up to about 15 mole percent of the substrate. Inone embodiment, the sulfur scavenger may be present in an amount in arange of from about 3 mole percent to about 10 mole percent of thesubstrate. In one embodiment, the sulfur scavenger is present in amountequal to or greater than about 5 mole percent of the substrate. In oneembodiment, the amount of sulfur scavenger present is about 9 molepercent of the catalyst substrate.

In a method of preparing the catalyst composition, a metal oxideprecursor, a catalyst metal precursor and an alkali metal precursor arereacted in the presence of a templating agent by hydrolysis andcondensation to form an intermediate that includes the metal oxide,alkali metal oxide, and catalyst metal. This intermediate is thencalcined to form a catalyst composition including a templated amorphousmetal oxide substrate having a plurality of pores, an alkali metaloxide, and catalyst metal. In one embodiment, the method describedresults in a catalyst composition, in which the alkali metal sulfurscavenger cation and the catalyst metal are dispersed in an intermixedform in the substrate metal oxide. The catalyst composition prepared bythis method provides results that are unexpectedly superior to moreconventionally prepared formulations.

In one embodiment, the metal-oxide precursors include inorganicalkoxides. Suitable inorganic alkoxides may include one or more oftetraethyl orthosilicate, tetramethyl orthosilicate, aluminumisopropoxide, aluminum tributoxide, aluminum ethoxide,aluminum-tri-sec-butoxide, aluminum tert-butoxide. In one embodiment,the inorganic alkoxide is aluminum sec-butoxide.

In various embodiments, the solvents include one or more solventsselected from aprotic polar solvents, polar protic solvents, andnon-polar solvents. Suitable aprotic polar solvents may includepropylene carbonate, ethylene carbonate, butyrolactone, acetonitrile,benzonitrile, nitromethane, nitrobenzene, sulfolane, dimethylformamide,N-methylpyrrolidone, or the like. Suitable polar protic solvents mayinclude water, nitromethane, acetonitrile, and short chain alcohols.Suitable short chain alcohols may include one or more of methanol,ethanol, propanol, isopropanol, butanol, or the like. Suitable non polarsolvents may include benzene, toluene, methylene chloride, carbontetrachloride, hexane, heptane, diethyl ether, or tetrahydrofuran. Inone embodiment, a combination of solvents may also be used. Selection ofthe type and amount of solvent may affect or control the amount ofporosity generated in the catalyst composition, as well as affect orcontrol other pore characteristics.

Modifiers may be used to control hydrolysis kinetics of the inorganicalkoxides. Suitable modifiers may include one or more ethyl acetoacetate(EA), ethylene glycol (EG), triethanolamine (TA), or the like.

The templating agents serve as templates and may facilitate theproduction of catalyst composition including templated amorphoussubstrate materials, catalyst metal, and alkali metals. The catalystcomposition obtained by the calcination of an intermediate productcontaining metal oxide-alkali metal oxide and catalyst metal may containdirectionally aligned pores. Control of the pore characteristic may, inturn, provide control of the particle size of catalytic metal byreducing the catalytic metal lability or propensity to agglomerate. Theparticle size of catalytic metal may be controlled, with respect to poreformation of the porous template, by controlling or affecting one ormore of pore size, pore distribution, pore spacing, or pore dispersity.

In one embodiment, the calcination is conducted at temperatures in arange from about 350 degrees Centigrade to about 800 degrees Centigrade.In another embodiment, the calcination is conducted at temperatures in arange from about 400 degrees Centigrade to about 700 degrees Centigrade.In yet another embodiment, the calcination is conducted at temperaturesin a range from about 450 degrees Centigrade to about 750 degreesCentigrade. In one embodiment, the calcination is conducted at atemperature of about 550 degrees Centigrade. In various embodiments, thecalcination may be conducted for a time period in a range from about 10minutes to about 30 minutes, from about 30 minutes to about 60 minutes,from about 60 minutes to about 1 hour, from about 1 hour to about 10hours, from about 10 hours to about 24 hours, or from about 24 hours toabout 48 hours.

In a method of removing sulfur from a catalytic reduction system, anexhaust stream is passed from an exhaust source, such as an internalcombustion engine, over the catalyst composition that includes, asdescribed previously, a templated amorphous metal oxide substrate, acatalyst material, and a sulfur scavenger. The exhaust stream reactswith the catalyst composition to form sulfates. During a desulfationstep, the sulfate formed decomposes to produce sulfur oxides, which areremoved from the system. In one embodiment, desulfation comprisesexposing the catalyst to a reducing environment at an effectivecombination of time and temperature to decompose sulfur-containingspecies on the catalyst into gaseous sulfur-containing species, such assulfur oxide species, leaving behind sulfur scavenging solid species(such as alkali metal oxide) on the catalyst.

Without being limited by theory, the inventors envisage a preferentialreactivity of sulfur scavenger to the sulfur, in comparison with thecatalyst metal reactivity with sulfur. In one embodiment, the sulfurscavenger preferentially reacts with the sulfur to form an alkalimetal-sulfur compound. In one embodiment, the alkali metal sulfurscavenger reacts with the SO₂ gas and forms alkali metal sulfatespreferentially over forming catalyst metal sulfate. In one example, thecatalyst composition includes templated amorphous alumina as asubstrate, silver as a catalyst, and lithium as a sulfur scavenger; thelithium cation reacts with SO₂ gas preferentially relative to silver oralumina, to form lithium sulfate. In general, the lithium sulfate ismore easily decomposable compared to silver sulfate. Therefore, duringoperation, the lithium sulfate formed will readily decompose to releaseSO₂ gas during desulfation. In one embodiment, desulfation is carriedout by flowing an excess amount of reductant (Cl:N>10) through thecatalytic system in the absence of either O₂ or NO at elevatedtemperatures, for example, from about 300° C.-650° C. In one embodiment,the catalyst was subjected to 5 ppm of SO₂ for 8 hours and subjected todesulfation. The desulfation method was able to remove greater than 90%of SO₂ at 650° C. when O₂ was absent and about 70%-80% of SO₂ at 650° C.when NO was absent. The desulfation conditions are unfavorable tore-absorb SO₂ gas by lithium, silver or alumina, and therefore the SO₂gas exits the reduction system.

While testing the performance of the catalyst system, inventorssurprisingly noticed that the alkali metal sulfur scavengers furtherassist in reducing undesirable byproducts of emission treatment releasedfrom the emission treatment system. By using alkali metal sulfurscavengers, more than 50% reduction in emission of HCN, CH₃CHO, and HCHOare recorded in the emission treatment system.

Along with substrate, catalyst metal, and sulfur scavenger, the catalystcomposition may also include a promoter for the catalytic reaction ofnitrogen oxide reduction. Non-limiting examples of the promoter mayinclude various metals or metal oxides. The promoter may include one ormore of indium, gallium, tin, silver, manganese, molybdenum, chromium,germanium, cobalt, nickel, gold, copper, iron, and their oxides. In oneembodiment, the sulfur scavenger alkali metal additionally acts as apromoter.

Along with the metals and metal oxides mentioned above, the catalystcomposition may further have additional cations dispersed or disposed onthe catalyst substrate that enhance hydrothermal stability of thecomposition and/or the catalytic activity of the catalyst metal. In oneembodiment, one or more additional cations may be selected from thegroup consisting of zirconium, iron, gallium, indium, tungsten, zinc,platinum, and rhodium. In one embodiment, the additional dopantcomprises zirconium.

In one embodiment, the catalyst composition can be included infabricating a catalytic surface. In one embodiment, the catalystcomposition can be shaped and formed as a catalyst surface. In anotherembodiment, a slurry of the catalyst composition in a liquid medium canbe formed and contacted with a catalyst support to form a catalyticreduction system with a washcoated monolith catalyst. Therefore, in oneembodiment, the catalytic reduction system comprises the catalystsupport and the catalytic composition comprising the templated amorphousmetal oxide substrate and the catalyst material.

A catalyst support can be in any form including foams, monoliths, andhoneycombs. Suitable materials for the catalyst support include ceramicsand metals. Examples of ceramics include oxides, such as alumina,silica, titanate compounds, as well as refractory oxides, cordierite,mullite, and zeolite. Other examples include metal carbides and metalnitrides. Carbon may be useful in some embodiments. In specificembodiments, the catalyst support includes silicon carbide, fusedsilica, activated carbon, or aluminum titanate. Zeolite, as used herein,includes hydrated aluminosilicates, such as analcime, chabazite,heulandite, natrolite, phillipsite, and stilbite. Mullite, as usedherein, is a form of aluminum silicate. In another exemplary embodiment,the suitable catalyst support includes metal corrugated forms.

In one embodiment, the slurry of the catalyst powder is washcoated ontoa catalyst support such as a monolith. In one embodiment of theinvention, the catalyst support is a monolith including cordierite. Theapplied washcoat may be dried, sintered and used to reduce emissioncontent such as NOx.

In a method of using the catalytic reduction system, the catalyticreduction system is disposed in the exhaust stream of an exhaust gassource, such as an internal combustion engine. An internal combustionengine may be part of any of a variety of mobile or fixed/stationaryassets, for example, an automobile, locomotive, or power generator.Because different engines have different combustion characteristics andbecause of the use of different fuels, the exhaust stream componentsdiffer from one system to another. Such differences may includevariations in NO_(x) levels, presence of sulfur, oxygen level, steamcontent, and the presence or quantity of other species of reactionproduct. Changes in the operating parameters of the engine may alsoalter the exhaust flow characteristics. Examples of differing operatingparameters may include temperature and flow rate. The catalyticreduction system may be used to reduce NO_(x) to nitrogen at a desirablerate and at a desirable temperature appropriate for the given system andoperating parameters.

In one method of using the catalytic reduction system, the catalyticreduction system is disposed in the exhaust stream of an internalcombustion engine. The catalyst composition of the catalytic reductionsystem reduces nitrogen oxides to nitrogen. The nitrogen oxide presentin the gas stream may be reduced at a temperature of about 250° C. orgreater. In one embodiment, the reduction occurs at a temperature rangeof about 250° C. to about 350° C. In another embodiment, the temperatureis in the range of about 350° C. to about 500° C. In another specificembodiment the temperature is in the range of about 500° C. to about600° C. In one exemplary embodiment, the nitrogen oxide present in thegas stream may be reduced at a temperature of less than about 350° C.

EXAMPLES

The following examples illustrate methods and embodiments in accordancewith exemplary embodiments, and as such should not be construed asimposing limitations upon the claims. All components are commerciallyavailable from common chemical suppliers.

Preparation of Materials

A 5000 mL 3-neck round bottom flask was set up with a mechanicalstirrer, reflux condenser, and addition funnel. About 6.51 g (38.5 mmol)of AgNO₃ and about 0.6 g (8.7 mmol) of LiNO₃ were dissolved in about 240mL water and added to the flask for preparing 4.4 mole % of Ag and 1 mol% of Li doping. Different lithium doping level may be achieved byvarying the addition of LiNO₃. Following the addition to the flask, themechanical stirrer was turned on and contents of flask were stirred.About 111.9 g of TRITON X-114 was mixed with heptane and added to theflask. The mixture was stirred for 30 minutes at a medium pace underambient conditions to obtain a white suspension. About 415 g (1.69 mol)of aluminum sec-butoxide (Al(O^(sec)Bu)₃) was added by charging a 1 Lpolyethylene jar whose cap was equipped with a gas inlet and a dip-tubeoutlet. Using 4-6 psi nitrogen, a feed of about 2.5 mL/min was achieved.Addition was complete after 180 min. The contents were heated to refluxfor 22 h. The solid was recovered by filtration and washed with ethanol.The obtained brown solid was then subjected to pyrolysis at 550° C.under nitrogen and then calcination in air at 550° C.

Catalyst Testing

After calcination, some powders were tested for fresh performance,performance after one hour of operation, performance after sulfation,and desulfation.

During the test, the catalyst composition was disposed in a reactor todetermine its nitrogen oxide conversion capabilities in a simulatedexhaust gas stream. An ultra-low sulfur diesel (ULSD) fuel having aboiling point of less than 210° C. was used as a reductant. Thereduction in NOx concentration relates to catalytic activity of thecatalyst compositions.

A simulated exhaust gas stream containing an exhaust gas composition wasused. The exhaust gas composition included 9 percent O₂, 300 parts permillion NO, 7 percent H₂O, and the balance N₂. The gas hour spacevelocity (GHSV) was about 30,000 hr⁻¹. For sulfation, about 5 ppm SO₂ isadded in nominal conditions and passed for 8 hours at 350° C. Fordesulfation, the gas composition included an oxygen concentrationvarying from zero to about 3 percent, about 300 parts per million of NO,7 percent H₂O, and balance N₂. The desulfation step was normally carriedout at a temperature varying from about 300° C. to about 500° C.

The temperature dependent NOx reduction activities of the differentcompositions at different test conditions are plotted as shown in FIG.1-16. The comparison of amount of byproducts of the emission treatmentsystem in the absence and presence of lithium sulfur scavenger isplotted in FIG. 17-18.

Test Results

FIG. 1 illustrates the NO_(x) activities of the fresh 4.5 mol % Ag-TAcatalyst composition without the addition of lithium, while FIG. 2, FIG.3, and FIG. 4 illustrate the NO_(x) activities of the fresh 4.5 mol %Ag-TA catalyst composition with 1%, 5%, and 14% respectively of Liaddition as a sulfur scavenger. Similarly, FIG. 5 illustrates the NOxacitivities of the 4.5 mol % Ag-TA catalyst composition without theaddition of lithium, after about an hour of operation, while FIG. 6,FIG. 7, and FIG. 8 illustrate the NO_(x) activities after one hour ofoperation of the 4.5 mol % Ag-TA catalyst composition with 1%, 5%, and14% respectively of Li addition as a sulfur scavenger.

FIG. 9 illustrates the NO_(x) activities of the sulfated fresh 4.5 mol %Ag-TA catalyst composition without the addition of lithium, while FIG.10, FIG. 11, and FIG. 12 illustrate the NO_(x) activities aftersulfation of the fresh 4.5 mol % Ag-TA catalyst composition with 1%, 5%,and 14% respectively of Li addition as a sulfur scavenger. Similarly,FIG. 13 illustrates the NOx acitivities of the 4.5 mol % Ag-TA catalystcomposition without the addition of lithium, after about an hour ofsulfation, while FIG. 14, FIG. 15, and FIG. 16 illustrate the NO_(x)activities after one hour of sulfation of the 4.5 mol % Ag-TA catalystcomposition with 1%, 5%, and 14% respectively of Li addition as a sulfurscavenger.

By comparing these graphs, it can be seen that during initial operationand during operation after sulfation, addition of 1% or 5% lithiumimproves NOx activity during initial stages and after one hour ofoperation. 1% and 5% lithium addition seem to be comparatively betterthan 14% Li addition. Between 1% and 5% lithium addition, 5% Li additioncomparatively improves the high temperature NOx activity of Ag-TAcatalyst.

FIG. 17 graphically illustrates the comparison of temperature dependentHCN byproduct formation in the absence and presence of 1% Li addition tothe Ag-TA catalyst. The HCN by product during NOx reduction over undoped4.5 mol % Ag-TA catalyst is about 30-70 ppm depending on the temperatureof operation, while for the Li doped 4.5 mol % Ag-TA catalyst only about0-5 ppm of HCN by products were determined

FIG. 18 compares the effect of Li addition in the formation of CH₃CHOand HCHO. It can be observed that the CH₃CHO formation reduces fromabout 40-130 ppm to a range of about 10-40 ppm after 1% Li addition. TheHCHO formation reduces from about 10-30 ppm to a range of about 5-10 ppmafter 1% Li addition.

The embodiments described herein are examples of composition, system,and methods having elements corresponding to the elements of theinvention recited in the claims. This written description may enablethose of ordinary skill in the art to make and use embodiments havingalternative elements that likewise correspond to the elements of theinvention recited in the claims. The scope of the invention thusincludes composition, system and methods that do not differ from theliteral language of the claims, and further includes other compositionsand articles with insubstantial differences from the literal language ofthe claims.

While only certain features and embodiments have been illustrated anddescribed herein, many modifications and changes may occur to one ofordinary skill in the relevant art. The appended claims cover all suchmodifications and changes.

1. A catalyst composition, comprising: a templated amorphous metal oxide substrate having a plurality of pores; a catalyst material comprising a catalyst metal and disposed on the substrate; and a sulfur scavenger comprising an alkali metal and disposed on the substrate.
 2. The composition of claim 1, wherein the alkali metal comprises lithium, sodium, or potassium.
 3. The composition of claim 2, wherein the alkali metal comprises lithium.
 4. The composition of claim 1, wherein the alkali metal is in an amount from about 0.1 mole percent to about 15 mole percent of the substrate.
 5. The composition of claim 4, wherein the alkali metal is in an amount from about 3 mole percent to about 10 mole percent of the substrate.
 6. The composition of claim 1, wherein the catalyst metal comprises silver.
 7. The composition of claim 1, wherein the templated amorphous metal oxide substrate comprises alumina, silica, aluminosilicate, or combination thereof.
 8. The composition of claim 1, wherein the substrate further comprises a dopant material selected from the group consisting of zirconium, iron, gallium, indium, tungsten, zinc, platinum, and rhodium.
 9. The composition of claim 1, wherein the catalyst material and sulfur scavenger are dispersed in an intermixed form in the substrate.
 10. A method of preparation of a catalyst composition, comprising: combining a metal oxide precursor, a catalyst metal precursor and an alkali metal precursor in the presence of a templating agent; hydrolyzing and condensing to form an intermediate product that comprises metal oxide, alkali metal oxide, and catalyst metal; and calcining to form a templated amorphous metal oxide substrate having a plurality of pores and comprising an alkali metal oxide and catalyst metal.
 11. A catalytic reduction system comprising: a catalyst support; a catalyst composition disposed on the catalyst support, the catalyst composition comprising: a templated amorphous metal oxide substrate having a plurality of pores; a catalyst material comprising a catalyst metal and disposed on the substrate; and a sulfur scavenger comprising an alkali metal and disposed on the substrate.
 12. The catalytic reduction system of claim 11, wherein the alkali metal comprises lithium.
 13. The catalytic reduction system of claim 11, wherein the alkali metal is in an amount from about 0.1 mole percent to about 15 mole percent based on the substrate.
 14. The catalytic reduction system of claim 13, wherein the alkali metal is in an amount from about 3 mole percent to about 10 mole percent based on the substrate.
 15. The catalytic reduction system of claim 11, wherein the catalyst metal comprises silver.
 16. A system comprising: an internal combustion engine, and a catalytic reduction system disposed to receive an exhaust stream from the engine, wherein the catalytic reduction system comprises a catalyst support; a catalyst composition disposed on the catalyst support, the catalyst composition comprising: a templated amorphous metal oxide substrate having a plurality of pores; a catalyst material comprising a catalyst metal and disposed on the substrate; and a sulfur scavenger comprising an alkali metal and disposed on the substrate.
 17. A method of removing sulfur from a catalytic reduction system, comprising: passing an exhaust stream from an exhaust source over a catalyst composition, wherein the catalyst composition comprises a templated amorphous metal oxide substrate, a catalyst material comprising a catalyst metal, and a sulfur scavenger; reacting the exhaust stream with the catalyst composition to form sulfates; decomposing the sulfates to produce sulfur oxides; and removing the sulfur oxides from the catalytic reduction system.
 18. The method of claim 17, wherein reacting the exhaust stream comprises reacting the exhaust stream with the sulfur scavenger of the catalyst composition to form the sulfates. 